Prove the identity:

Replace
on left side by
Replace
on left side by
Combine the numerators over the common denominator:
Form the conjugate of the numerator by changing the sign
of the second term:
, put it over itself,
like this
, which equals 1,
so we can multiply by it without changing the value:
Indicate the multiplications of the tops and bottoms:
FOIL out the top:
Simplify by canceling in the top:
Replace
by
The
in the bottom cancels out the
square in the top:
Edwin